In pulse‐type ultrasonic testing, the size of the defect or flaw in a specimen is estimated by the size of the echo reflected by the defect of flaw. By this method, the acceptability of the specimen is determined. In today's ultrasonic flaw detecting, the reflection coefficient of flaws, the characteristics of the acoustic field, the echoes from flaws in specimens, etc., are handled as those of continuous waves. However, in order to improve the resolving power, which is one of the flaw‐detecting capabilities of the ultrasonic flaw‐detecting method, it is necessary to minimize the number of waves contained in the pulses, and because of this the frequency distribution becomes wide. Under a condition such as this, it is not possible to determine the quantitativeness of echo from a flaw. With respect to the above problem, the author conducted a study especially on the probe, transmitter, receiver amplifier, etc., of the apparatus used in pulse‐type ultrasonic testing, mainly in order to obtain the quantitativeness of the echoes reflected by flaws.